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/*
* Copyright (C) 2013 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.android.documentsui;
import android.content.AsyncTaskLoader;
import android.content.Context;
import android.database.ContentObserver;
import android.os.CancellationSignal;
import android.os.OperationCanceledException;
/**
* Loader that derives its data from a Uri. Watches for {@link ContentObserver}
* changes while started, manages {@link CancellationSignal}, and caches
* returned results.
*/
public abstract class UriDerivativeLoader<P, R> extends AsyncTaskLoader<R> {
final ForceLoadContentObserver mObserver;
private final P mParam;
private R mResult;
private CancellationSignal mCancellationSignal;
@Override
public final R loadInBackground() {
synchronized (this) {
if (isLoadInBackgroundCanceled()) {
throw new OperationCanceledException();
}
mCancellationSignal = new CancellationSignal();
}
try {
return loadInBackground(mParam, mCancellationSignal);
} finally {
synchronized (this) {
mCancellationSignal = null;
}
}
}
public abstract R loadInBackground(P param, CancellationSignal signal);
@Override
public void cancelLoadInBackground() {
super.cancelLoadInBackground();
synchronized (this) {
if (mCancellationSignal != null) {
mCancellationSignal.cancel();
}
}
}
@Override
public void deliverResult(R result) {
if (isReset()) {
closeQuietly(result);
return;
}
R oldResult = mResult;
mResult = result;
if (isStarted()) {
super.deliverResult(result);
}
if (oldResult != null && oldResult != result) {
closeQuietly(oldResult);
}
}
public UriDerivativeLoader(Context context, P param) {
super(context);
mObserver = new ForceLoadContentObserver();
mParam = param;
}
@Override
protected void onStartLoading() {
if (mResult != null) {
deliverResult(mResult);
}
if (takeContentChanged() || mResult == null) {
forceLoad();
}
}
@Override
protected void onStopLoading() {
cancelLoad();
}
@Override
public void onCanceled(R result) {
closeQuietly(result);
}
@Override
protected void onReset() {
super.onReset();
// Ensure the loader is stopped
onStopLoading();
closeQuietly(mResult);
mResult = null;
getContext().getContentResolver().unregisterContentObserver(mObserver);
}
private void closeQuietly(R result) {
if (result instanceof AutoCloseable) {
try {
((AutoCloseable) result).close();
} catch (RuntimeException rethrown) {
throw rethrown;
} catch (Exception ignored) {
}
}
}
}
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